Method and apparatus for defining resource elements for the provision of channel state information reference signals

ABSTRACT

Methods, apparatus and computer program products define additional resource elements of a physical resource block (PRB) to be allocated for the provision of channel state information reference signals in a manner that does not create issues relating to backwards compatibility for legacy mobile terminals. A method may include receiving a definition of a plurality of resource elements of a PRB to be allocated for provision of channel state information reference signals. At least some of the plurality of resource elements of the PRB that are allocated for the provision of channel state information reference signals correspond in position to resource elements of the PRB that are interpreted by a different type of mobile terminal to be muted. The method also causes, channel state information reference signals to be received via the plurality of resource elements of the PRB that are allocated for the provision of channel state information reference signals.

TECHNOLOGICAL FIELD

Embodiments of the present invention relate generally to communicationstechnology and, more particularly, to methods and apparatus for defininga plurality of resource elements for the provision of channel stateinformation reference signals

BACKGROUND

Some wireless communications systems utilize multiple-input andmultiple-output (MIMO) technology. MIMO technology involves the use ofmultiple antennas for both the transmitter and a receiver so as toimprove communication performance, such as by offering significantincreases in data throughput and link range without additional bandwidthor transmit power as a result of its higher spectral efficiency asmeasured, for example, in bits per second per hertz of bandwidth, andlink reliability or diversity. For example, systems that operate inaccordance with Releases 8, 9 and 10 of the Long Term Evolution (LTE)specification support MIMO, that is, MIMO transmissions from a transmitpoint (which can be also represented by a base station, such as aevolved node B(eNB)), to one or more mobile terminals. Indeed, Releases8 and 9 of the LTE specification support four stream transmission, whichcould result in 4×4 MIMO in the context of four transmission (Tx)antennas and four reception antennas. In addition, one stream and twostream beamforming from a maximum of 8Tx antennas have been introducedin Release 8 and Release 9, respectively. Release 10 of the LTEspecifications extends support for downlink MIMO for up to eight streamtransmissions and therefore up to at least 8×8 MIMO in the context ofeight transmission antennas and eight reception antennas. Additionally,Release 10 of the LTE specification provides enhanced support formulti-user MIMO as well as support for seamless switching between singleand multi-user MIMO.

To facilitate closed-loop MIMO communications, reference signals may beused for channel state information estimation. This is especially validin frequency division duplexing (FDD) systems where channel reciprocitycannot be exploited, as it is the case in time division duplexing (TDD).For example, in the context of downlink MIMO, channel state informationfeedback may be provided via channel state information reference signalsfrom a mobile terminal to the transmit point. The channel stateinformation reference signals may be transmitted periodically, may havea low overhead and high reuse factors, especially in instances in whichthe number of transmission antennas is relatively low. Reference signalsare mapped to the transmit point antenna ports. Antenna ports may have aone to one mapping to the physical transmit antennas of the transmitpoint, or may characterize multiple transmit antennas of one transmitpoint. Indeed, Release 10 of the LTE specification includes channelstate information reference signals (CSI-RS) as well as physicaldownlink shared channel (PDSCH) resource element (RE) muting, whichcomplement the CSI-RS operation in an instance in which accurateinter-cell channel estimation is desired. All LTE Releases make use alsoof Common Reference Signals (CRS) which are sent in every subframe andmay characterize a maximum of 4 antenna ports.

By way of example, FIG. 1 illustrates resource elements usage for normalcyclic prefix (CP) in frame structure type 1 (which applies to FDD) asspecified in Release 10 of the LTE specification for one physicalresource block (PRB). As shown in FIG. 1, resource elements, that is,respective elements of the orthogonal frequency division multiplexing(OFDM) time frequency grid represented by the PRB, may be allocated forcommon reference signals (CRS) ports #1 and #2, CRS ports #3 and #4,demodulation reference signal (DMRS), port #5 if so configured forRelease 8 of the LTE specifications, DMRS for Releases 9 and 10 of theLTE specifications, physical downlink control channel (PDCCH) andphysical downlink shared channel (PDSCH). The physical resource blockalso includes resource elements allocated for CSI-RS. In this regard,the CSI-RS resource elements are designated with numbers, e.g., 0, 1, .. . 7, with the alphabetical suffixes, e.g., a, b, . . . t, indicatingthe different transmit points to which the CSI-RS resource elements aredirected. For example, the 0_(b), 1_(b) resource elements are a pair ofCSI-RS resource elements mapped to the transmit antennas of a transmitpoint. They can be indicated in a dedicated way to one or more mobileterminals

The density of the CSI-RS pattern in accordance with Release 10 of theLTE specification is one CSI-RS resource element per antenna port perPRB. By way of example, FIG. 1 illustrates the PRBs for two antennaports, four antenna ports and eight antenna ports with two REs, four REsand eight REs allocated for CSI-RS, respectively. Similarly, FIG. 2illustrates the CSI-RS pattern for extended CP in frame structure type 1(FDD) specified in Release 10 of the LTE specification for one PRB. Asdescribed above in conjunction with FIG. 1, FIG. 2 illustrates the PRBsfor two antenna ports, four antenna ports and eight antenna ports.Further, FIG. 3 a illustrates the CSI-RS pattern for normal CP in framestructure type 2 (which applies to TDD), while FIG. 3 b illustrates theCSI-RS pattern for extended CP in frame structure type 2 (TDD) withthese patterns being utilized in addition to the patterns utilized forframe structure type 1, as shown in FIGS. 1 and 2.

PDSCH RE muting is used in a complementary way to the CSI-RS if accurateinter-transmit points channel state information is desired. The sameCSI-RS patterns are used for the muted REs.

The density of one RE for CSI-RS per PRB per port may be sufficient forsingle-cell CSI estimation which may, in turn, allow the base station tocontrol the antenna weights to achieve a precoding gain. However, it maybe desired for the mobile terminal to provide feedback information notonly regarding CSI estimation, but also regarding interference, such asthe interference covariance matrix that may be required for channelquality indication (CQI) and rank estimation. In this regard, thedensity of one resource element for CSI-RS per PRB per port may beinsufficient for interference covariance estimation or, at least, maylead to an undesirably large error in the estimation of the interferencecovariance which, in turn, may cause erroneous CQI and erroneous rankfeedback which may lead to a poor selection of transmission scheme, bothmodulation and coding scheme (MCS) and rank, by the base station. Thesepoor selections may, in turn, lead to throughput loss at the systemlevel.

In Release 10 of the LTE specification, the mobile terminal may rely onCRS for interference estimation. However, CRS may have a reuse factor of3 with two or more transmission antennas such that CRS collisions ofneighboring cells are unlikely to be avoided. This scenario may causeless accurate CQI and rank estimation in typical fractional loadscenarios than is desired. Thus, CQI and rank estimation could benefitby the use of CSI-RS. However, the current CSI-RS density is too low toprovide the desired channel state information/interference accuracy.

Furthermore, there is an ongoing effort to support heterogeneousnetworks which exhibit difficult interference characteristics. Thus,there is a tendency in 3^(rd) Generation Partnership Project (3GPP)networks to reduce CRS usage, as CRS may be problematic from theinter-cell interference perspective. In a backwards compatible manner,this CRS reduction can be accomplished, for example, with MultimediaBroadcast over a Single Frequency Network (MBSFN) sub-frames or by thedefinition of new extension carriers (without CRS) in relation tocarrier aggregation. Additionally, the reference signals provided byrelease 10 of the LTE specifications, such as the CSI-RS, have arelatively low overhead with respect to CRS, which provides a furtherincentive to limit the role of CRS going forward. Additionally, intransmission mode 9 of Release 10 of the LTE specification, the numberof CRS can be adjusted by turning off some of the ports, therebypotentially leading to the utilization of only one CRS port at aminimum. As such, it cannot be assumed that the mobile terminal willalways have sufficient CRS to perform interference estimation in thefuture.

Coordinated multi-point transmission (COMP) will require a mobileterminal to measure from the CSI-RS the channel from transmission pointsthat are geographically separated from a reference transmission point,such as a serving cell. These measurements may include propagation delaydifferences that show up in the effective frequency-domain channel as anadditional linear phase rotation. Thus, the mobile terminal may berequired to estimate a more frequency-selective channel and/or toestimate the timing differences between the different transmissionpoints. Such estimation and the subsequent feedback to the base stationwould also require more use of the reference signals, such as theCSI-RS, and a greater density of the reference signals within a PRB.

Notwithstanding the potential for increased utilization of the CSI-RS,efforts to simply increase the density of the reference signals, such asthe CSI-RS, within a PRB in order to support the additional feedbackthat is desired creates backwards compatibility issues with legacymobile terminals, such as those mobile terminals that operate inaccordance with prior releases of a respective specification. In thisregard, since these legacy mobile terminals would not be aware of theadditional reference signal transmissions, such as the additionalCSI-RS, the additional reference signal transmissions maydisadvantageously interfere with data transmissions of the legacy mobileterminals.

BRIEF SUMMARY

Methods, apparatus and computer program products are provided accordingto an example embodiment for defining additional resource elements of aphysical resource block (PRB) to be allocated for the provision ofchannel state information reference signals in a manner that does notcreate issues relating to backwards compatibility for legacy mobileterminals, such as those that operate in accordance with Release 10 ofthe LTE specification. In one example, the methods, apparatus andcomputer program products increase the density of the resource elementsof a PRB that are allocated for the provision of channel stateinformation reference signals, such as the CSI-RS density, so as tofacilitate the provision of additional reference signals including, forexample, channel estimation and feedback relating to interferencecovariance estimation.

In one embodiment, a method is provided that includes receiving adefinition of a plurality of resource elements of a physical resourceblock (PRB) to be allocated for provision of channel state informationreference signals. At least some of the plurality of resource elementsof the PRB that are allocated for the provision of channel stateinformation reference signals correspond in position to resourceelements that are configured to be interpreted as muted by a differenttype of mobile terminal. The method of this embodiment also causes, witha processor, channel state information reference signals to be receivedvia the plurality of resource elements of the PRB that are allocated forthe provision of channel state information reference signals.

In another embodiment, an apparatus is provided that includes at leastone processor and at least one memory including computer program codewith the at least one memory and the computer program code beingconfigured to, with the at least one processor, cause the apparatus atleast to receive a definition of a plurality of resource elements of aphysical resource block (PRB) to be allocated for provision of channelstate information reference signals. At least some of the plurality ofresource elements of the PRB that are allocated for the provision ofchannel state information reference signals correspond in position toresource elements that are configured to be interpreted as muted by adifferent type of mobile terminal. The at least one memory and thecomputer program code of one embodiment are also configured to, with theat least one processor, cause the apparatus to cause channel stateinformation reference signals to be received via the plurality ofresource elements of the PRB that are allocated for the provision ofchannel state information reference signals.

In a further embodiment, a computer program product is provided thatincludes at least one computer-readable storage medium havingcomputer-executable program code instructions stored therein with thecomputer-executable program code instructions including program codeinstructions for receiving a definition of a plurality of resourceelements of a physical resource block (PRB) to be allocated forprovision of channel state information reference signals. At least someof the plurality of resource elements of the PRB that are allocated forthe provision of channel state information reference signals correspondin position to resource elements that are configured to be interpretedas muted by a different type of mobile terminal. The computer-executableprogram code instructions of this embodiment also include program codeinstructions for causing channel state information reference signals tobe received via the plurality of resource elements of the PRB that areallocated for the provision of channel state information referencesignals.

In yet another embodiment, an apparatus is provided that includes meansfor receiving a definition of a plurality of resource elements of aphysical resource block (PRB) to be allocated for provision of channelstate information reference signals. At least some of the plurality ofresource elements of the PRB that are allocated for the provision ofchannel state information reference signals correspond in position toresource elements that are configured to be interpreted as muted by adifferent type of mobile terminal. The apparatus of this embodiment alsoincludes means for causing channel state information reference signalsto be received via the plurality of resource elements of the PRB thatare allocated for the provision of channel state information referencesignals.

In one embodiment, a method is provided that includes defining one ormore first resource elements of a physical resource block (PRB) to beallocated for provision of channel state information reference signalsfrom a first type of mobile terminal. The method of this embodiment alsodefines one or more second resource elements of the PRB to beinterpreted as muted by the first type of mobile terminal. The methodalso defines, via a processor, a plurality of resource elements of thePRB to be allocated for provision of channel state information referencesignals from a second type of mobile terminal. At least some of theplurality of resource elements of the PRB that are allocated for theprovision of channel state information reference signals correspond inposition to the second resource elements of the PRB, thereby overlappingin one embodiment on exactly the same positions as the muted resourceelements of the first type of mobile terminal.

In another embodiment, an apparatus is provided that includes at leastone processor and at least one memory including computer program codewith the at least one memory and the computer program code beingconfigured to, with the at least one processor, cause the apparatus atleast to define one or more first resource elements of a physicalresource block (PRB) to be allocated for provision of channel stateinformation reference signals from a first type of mobile terminal. Theat least one memory and the computer program code of one embodiment arealso configured to, with the at least one processor, cause the apparatusto define one or more second resource elements of the PRB to beinterpreted as muted by the first type of mobile terminal. The at leastone memory and the computer program code of one embodiment are alsoconfigured to, with the at least one processor, cause the apparatus todefine a plurality of resource elements of the PRB to be allocated forprovision of channel state information reference signals from a secondtype of mobile terminal. At least some of the plurality of resourceelements of the PRB that are allocated for the provision of channelstate information reference signals correspond in position to the secondresource elements of the PRB, thereby overlapping in one embodiment onexactly the same positions as the muted resource elements of the firsttype of mobile terminal.

In a further embodiment, a computer program product is provided thatincludes at least one computer-readable storage medium havingcomputer-executable program code instructions stored therein with thecomputer-executable program code instructions including program codeinstructions for defining one or more first resource elements of aphysical resource block (PRB) to be allocated for provision of channelstate information reference signals from a first type of mobileterminal. The computer-executable program code instructions may alsoinclude program code instructions for defining one or more secondresource elements of the PRB to be interpreted as muted by the firsttype of mobile terminal. The computer-executable program codeinstructions may also include program code instructions for defining aplurality of resource elements of the PRB to be allocated for provisionof channel state information reference signals from the second type ofmobile terminal. At least some of the plurality of resource elements ofthe PRB that are allocated for the provision of channel stateinformation reference signals correspond in position to the secondresource elements of the PRB, thereby overlapping in one embodiment onexactly the same positions as the muted resource elements of the firsttype of mobile terminal.

In yet another embodiment, an apparatus is provided that includes meansfor defining one or more first resource elements of a physical resourceblock (PRB) to be allocated for provision of channel state informationreference signals from a first type of mobile terminal. The apparatus ofthis embodiment also includes means for defining one or more secondresource elements of the PRB to be interpreted as muted by the firsttype of mobile terminal. The apparatus also includes means for defininga plurality of resource elements of the PRB to be allocated forprovision of channel state information reference signals from the secondtype of mobile terminal. At least some of the plurality of resourceelements of the PRB that are allocated for the provision of channelstate information reference signals correspond in position to the secondresource elements of the PRB, thereby overlapping in one embodiment onexactly the same positions as the muted resource elements of the firsttype of mobile terminal.

The above summary is provided merely for purposes of summarizing someexample embodiments of the invention so as to provide a basicunderstanding of some aspects of the invention. Accordingly, it will beappreciated that the above described example embodiments are merelyexamples and should not be construed to narrow the scope or spirit ofthe invention in any way. It will be appreciated that the scope of theinvention encompasses many potential embodiments, some of which will befurther described below, in addition to those here summarized.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Having thus described example embodiments of the invention in generalterms, reference will now be made to the accompanying drawings, whichare not necessarily drawn to scale, and wherein:

FIG. 1 illustrates the physical resource blocks (PRBs) for normal CP inframe structure type 1 for a system having two antenna ports, fourantenna ports and eight antenna ports;

FIG. 2 illustrates the PRBs for extended CP in frame structure type 1for a system having two antenna ports, four antenna ports and eightantenna ports;

FIG. 3 a illustrates the PRBs for a normal CP in frame structure type 2;

FIG. 3 b illustrates the PRBs for an extended CP in frame structure type2;

FIG. 4 illustrates a system including a mobile terminal and a basestation configured to support communications in accordance with oneembodiment of the present invention;

FIG. 5 is a block diagram of a mobile terminal in accordance with oneembodiment of the present invention;

FIG. 6 is a block diagram of a base station or other network element inaccordance with one embodiment of the present invention;

FIG. 7 is a flow chart illustrating the operations performed from theperspective of a mobile terminal in accordance with one embodiment ofthe current invention;

FIG. 8 a is the PRB that is defined for a legacy mobile\terminal havingone or two antenna ports in accordance with one embodiment of thepresent invention;

FIG. 8 b is the PRB that is defined for a mobile terminal having one ortwo antenna ports in accordance with one embodiment of the presentinvention;

FIG. 9 a is the PRB that is defined for a legacy mobile\terminal havingfour antenna ports in accordance with one embodiment of the presentinvention;

FIG. 9 b is the PRB that is defined for a mobile terminal having fourantenna ports in accordance with one embodiment of the presentinvention; and

FIG. 10 is a flow chart illustrating the operations performed from theperspective of a base station or other network element in accordancewith one embodiment of the current invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the inventions are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

As used in this application, the term ‘circuitry’ refers to all of thefollowing: (a) hardware-only circuit implementations (such asimplementations in only analog and/or digital circuitry) and (b) tocombinations of circuits and software (and/or firmware), such as (asapplicable): (i) to a combination of processor(s) or (ii) to portions ofprocessor(s)/software (including digital signal processor(s)), software,and memory(ies) that work together to cause an apparatus, such as amobile phone or server, to perform various functions) and (c) tocircuits, such as a microprocessor(s) or a portion of amicroprocessor(s), that require software or firmware for operation, evenif the software or firmware is not physically present.

This definition of ‘circuitry’ applies to all uses of this term in thisapplication, including in any claims. As a further example, as used inthis application, the term “circuitry” would also cover animplementation of merely a processor (or multiple processors) or portionof a processor and its (or their) accompanying software and/or firmware.The term “circuitry” would also cover, for example and if applicable tothe particular claim element, a baseband integrated circuit orapplications processor integrated circuit for a mobile phone or asimilar integrated circuit in server, a cellular network device, orother network device.

A method, apparatus and computer program product are disclosed fordefining a plurality of resource elements for the provision of channelstate information reference signals. In this regard, the method,apparatus and computer program product of some example embodimentsdefine the plurality of resource elements for the provision of channelstate information reference signals without interfering with theoperation of legacy mobile terminals. Although the method, apparatus andcomputer program product may be implemented in a variety of differentsystems, one example of such a system is shown in FIG. 4, which includesa first communication device (e.g., mobile terminal 10) that is capableof communication with a network 12 (e.g., a core network) via a transmitpoint 14 (e.g., an evolved Node B (eNB) or an array of antennasconnected to an eNB). While the network may be configured in accordancewith LTE or LTE-Advanced (LTE-A), other networks may support the method,apparatus and computer program product of embodiments of the presentinvention including those configured in accordance with wideband codedivision multiple access (W-CDMA), CDMA2000, global system for mobilecommunications (GSM), general packet radio service (GPRS) and/or thelike.

The network 12 may include a collection of various different nodes,devices or functions that may be in communication with each other viacorresponding wired and/or wireless interfaces. For example, the networkmay include one or more transmit points 14, each of which may serve acoverage area divided into one or more cells. The transmit points orother communication node could be, for example, part of one or morecellular or mobile networks or public land mobile networks (PLMNs). Inturn, other devices such as processing devices (e.g., personalcomputers, server computers or the like) may be coupled to the mobileterminal and/or the second communication device via the network.

A communication device, such as the mobile terminal 10 (also known asuser equipment (UE)), may be in communication with other communicationdevices or other devices via the transmit point 14 and, in turn, thenetwork 12. In some cases, the communication device may include anantenna for transmitting signals to and for receiving signals from atransmit point.

In some example embodiments, the mobile terminal 10 may be a mobilecommunication device such as, for example, a mobile telephone, portabledigital assistant (PDA), pager, laptop computer, or any of numerousother hand held or portable communication devices, computation devices,content generation devices, content consumption devices, or combinationsthereof. As such, the mobile terminal may include one or more processorsthat may define processing circuitry either alone or in combination withone or more memories. The processing circuitry may utilize instructionsstored in the memory to cause the mobile terminal to operate in aparticular way or execute specific functionality when the instructionsare executed by the one or more processors. The mobile terminal may alsoinclude communication circuitry and corresponding hardware/software toenable communication with other devices and/or the network 12.

In one embodiment, for example, the mobile terminal 10 may be embodiedas or otherwise include an apparatus 20 as generically represented bythe block diagram of FIG. 5. In the context of a mobile terminal, theapparatus may be configured to define a plurality of resource elementsfor the provision of channel state information reference signals. Whilethe apparatus may be employed, for example, by a mobile terminal, itshould be noted that the components, devices or elements described belowmay not be mandatory and thus some may be omitted in certainembodiments. Additionally, some embodiments may include further ordifferent components, devices or elements beyond those shown anddescribed herein.

As shown in FIG. 5, the apparatus 20 may include or otherwise be incommunication with processing circuitry 22 that is configurable toperform actions in accordance with example embodiments described herein.The processing circuitry may be configured to perform data processing,application execution and/or other processing and management servicesaccording to an example embodiment of the present invention. In someembodiments, the apparatus or the processing circuitry may be embodiedas a chip or chip set. In other words, the apparatus or the processingcircuitry may comprise one or more physical packages (e.g., chips)including materials, components and/or wires on a structural assembly(e.g., a baseboard). The structural assembly may provide physicalstrength, conservation of size, and/or limitation of electricalinteraction for component circuitry included thereon. The apparatus orthe processing circuitry may therefore, in some cases, be configured toimplement an embodiment of the present invention on a single chip or asa single “system on a chip.” As such, in some cases, a chip or chipsetmay constitute means for performing one or more operations for providingthe functionalities described herein.

In an example embodiment, the processing circuitry 22 may include aprocessor 24 and memory 26 that may be in communication with orotherwise control a device interface 28 and, in some cases, a userinterface 30. As such, the processing circuitry may be embodied as acircuit chip (e.g., an integrated circuit chip) configured (e.g., withhardware, software or a combination of hardware and software) to performoperations described herein. However, in some embodiments taken in thecontext of the mobile terminal 10, the processing circuitry may beembodied as a portion of a mobile computing device or other mobileterminal.

The user interface 30 (if implemented) may be in communication with theprocessing circuitry 22 to receive an indication of a user input at theuser interface and/or to provide an audible, visual, mechanical or otheroutput to the user. As such, the user interface may include, forexample, a keyboard, a mouse, a joystick, a display, a touch screen, amicrophone, a speaker, and/or other input/output mechanisms.

The device interface 28 may include one or more interface mechanisms forenabling communication with other devices and/or networks. In somecases, the device interface may be any means such as a device orcircuitry embodied in either hardware, or a combination of hardware andsoftware that is configured to receive and/or transmit data from/to anetwork 12 and/or any other device or module in communication with theprocessing circuitry 22. In this regard, the device interface mayinclude, for example, an antenna (or multiple antennas) and supportinghardware and/or software for enabling communications with a wirelesscommunication network and/or a communication modem or otherhardware/software for supporting communication via cable, digitalsubscriber line (DSL), universal serial bus (USB), Ethernet or othermethods.

In an example embodiment, the memory 26 may include one or morenon-transitory memory devices such as, for example, volatile and/ornon-volatile memory that may be either fixed or removable. The memorymay be configured to store information, data, applications, instructionsor the like for enabling the apparatus 20 to carry out various functionsin accordance with example embodiments of the present invention. Forexample, the memory could be configured to buffer input data forprocessing by the processor 24. Additionally or alternatively, thememory could be configured to store instructions for execution by theprocessor. As yet another alternative, the memory may include one of aplurality of databases that may store a variety of files, contents ordata sets. Among the contents of the memory, applications may be storedfor execution by the processor in order to carry out the functionalityassociated with each respective application. In some cases, the memorymay be in communication with the processor via a bus for passinginformation among components of the apparatus.

The processor 24 may be embodied in a number of different ways. Forexample, the processor may be embodied as various processing means suchas one or more of a microprocessor or other processing element, acoprocessor, a controller or various other computing or processingdevices including integrated circuits such as, for example, an ASIC(application specific integrated circuit), an FPGA (field programmablegate array), or the like. In an example embodiment, the processor may beconfigured to execute instructions stored in the memory 26 or otherwiseaccessible to the processor. As such, whether configured by hardware orby a combination of hardware and software, the processor may representan entity (e.g., physically embodied in circuitry—in the form ofprocessing circuitry 22) capable of performing operations according toembodiments of the present invention while configured accordingly. Thus,for example, when the processor is embodied as an ASIC, FPGA or thelike, the processor may be specifically configured hardware forconducting the operations described herein. Alternatively, as anotherexample, when the processor is embodied as an executor of softwareinstructions, the instructions may specifically configure the processorto perform the operations described herein.

As noted above, a transmit point 14 or other network entity may beconfigured to communicate with the mobile terminal 10. In some cases,the transmit point may include an antenna or an array of antennas fortransmitting signals to and for receiving signals from the mobileterminal. The transmit point may be embodied as a base station or may becommunicably connected to a base station with the base station includingone or more processors that may define processing circuitry either aloneor in combination with one or more memories. The processing circuitrymay utilize instructions stored in the memory to cause the base stationto operate in a particular way or execute specific functionality whenthe instructions are executed by the one or more processors. Thetransmit point may also include communication circuitry andcorresponding hardware/software to enable communication with the mobileterminal and/or the network 12.

In one embodiment in which the transmit point 14 is in communicationwith a base station, such as an eNB, an access point or the like, thebase station may be embodied as or otherwise include an apparatus 40 asgenerically represented by the block diagram of FIG. 6. While theapparatus may be employed, for example, by a base station, it should benoted that the components, devices or elements described below may notbe mandatory and thus some may be omitted in certain embodiments.Additionally, some embodiments may include further or differentcomponents, devices or elements beyond those shown and described herein.

As shown in FIG. 6, the apparatus 40 may include or otherwise be incommunication with processing circuitry 42 that is configurable toperform actions in accordance with example embodiments described herein.The processing circuitry may be configured to perform data processing,application execution and/or other processing and management servicesaccording to an example embodiment of the present invention. In someembodiments, the apparatus or the processing circuitry may be embodiedas a chip or chip set. In other words, the apparatus or the processingcircuitry may comprise one or more physical packages (e.g., chips)including materials, components and/or wires on a structural assembly(e.g., a baseboard). The structural assembly may provide physicalstrength, conservation of size, and/or limitation of electricalinteraction for component circuitry included thereon. The apparatus orthe processing circuitry may therefore, in some cases, be configured toimplement an embodiment of the present invention on a single chip or asa single “system on a chip.” As such, in some cases, a chip or chipsetmay constitute means for performing one or more operations for providingthe functionalities described herein.

In an example embodiment, the processing circuitry 42 may include aprocessor 44 and memory 46 that may be in communication with orotherwise control a device interface 48. As such, the processingcircuitry may be embodied as a circuit chip (e.g., an integrated circuitchip) configured (e.g., with hardware, software or a combination ofhardware and software) to perform operations described herein. However,in some embodiments taken in the context of the base station, theprocessing circuitry may be embodied as a portion of a base station orother network entity.

The device interface 48 may include one or more interface mechanisms forenabling communication with other devices and/or networks. In somecases, the device interface may be any means such as a device orcircuitry embodied in either hardware, or a combination of hardware andsoftware that is configured to receive and/or transmit data from/to anetwork 12 and/or any other device or module in communication with theprocessing circuitry 42. In this regard, the device interface mayinclude, for example, an antenna (or multiple antennas) and supportinghardware and/or software for enabling communications with a wirelesscommunication network and/or a communication modem or otherhardware/software for supporting communication via cable, digitalsubscriber line (DSL), universal serial bus (USB), Ethernet or othermethods.

In an example embodiment, the memory 46 may include one or morenon-transitory memory devices such as, for example, volatile and/ornon-volatile memory that may be either fixed or removable. The memorymay be configured to store information, data, applications, instructionsor the like for enabling the apparatus 40 to carry out various functionsin accordance with example embodiments of the present invention. Forexample, the memory could be configured to buffer input data forprocessing by the processor 44. Additionally or alternatively, thememory could be configured to store instructions for execution by theprocessor. As yet another alternative, the memory may include one of aplurality of databases that may store a variety of files, contents ordata sets. Among the contents of the memory, applications may be storedfor execution by the processor in order to carry out the functionalityassociated with each respective application. In some cases, the memorymay be in communication with the processor via a bus for passinginformation among components of the apparatus.

The processor 44 may be embodied in a number of different ways. Forexample, the processor may be embodied as various processing means suchas one or more of a microprocessor or other processing element, acoprocessor, a controller or various other computing or processingdevices including integrated circuits such as, for example, an ASIC(application specific integrated circuit), an FPGA (field programmablegate array), or the like. In an example embodiment, the processor may beconfigured to execute instructions stored in the memory 46 or otherwiseaccessible to the processor. As such, whether configured by hardware orby a combination of hardware and software, the processor may representan entity (e.g., physically embodied in circuitry—in the form ofprocessing circuitry 42) capable of performing operations according toembodiments of the present invention while configured accordingly. Thus,for example, when the processor is embodied as an ASIC, FPGA or thelike, the processor may be specifically configured hardware forconducting the operations described herein. Alternatively, as anotherexample, when the processor is embodied as an executor of softwareinstructions, the instructions may specifically configure the processorto perform the operations described herein.

Referring now to FIGS. 7 and 10, flowcharts illustrating the operationsperformed by a method, apparatus and computer program product, such asapparatus 20 of FIG. 3 in regards to FIG. 7 and apparatus 40 of FIG. 4in regards to FIG. 10, in accordance with one embodiment of the presentinvention are illustrated. It will be understood that each block of theflowchart, and combinations of blocks in the flowchart, may beimplemented by various means, such as hardware, firmware, processor,circuitry and/or other device associated with execution of softwareincluding one or more computer program instructions. For example, one ormore of the procedures described above may be embodied by computerprogram instructions. In this regard, the computer program instructionswhich embody the procedures described above may be stored by a memorydevice of an apparatus employing an embodiment of the present inventionand executed by a processor in the apparatus. As will be appreciated,any such computer program instructions may be loaded onto a computer orother programmable apparatus (e.g., hardware) to produce a machine, suchthat the resulting computer or other programmable apparatus provides forimplementation of the functions specified in the flowchart block(s).These computer program instructions may also be stored in anon-transitory computer-readable storage memory that may direct acomputer or other programmable apparatus to function in a particularmanner, such that the instructions stored in the computer-readablestorage memory produce an article of manufacture, the execution of whichimplements the function specified in the flowchart block(s). Thecomputer program instructions may also be loaded onto a computer orother programmable apparatus to cause a series of operations to beperformed on the computer or other programmable apparatus to produce acomputer-implemented process such that the instructions which execute onthe computer or other programmable apparatus provide operations forimplementing the functions specified in the flowchart block(s). As such,the operations of FIGS. 7 and 10, when executed, convert a computer orprocessing circuitry into a particular machine configured to perform anexample embodiment of the present invention. Accordingly, the operationsof each of FIGS. 7 and 10 define an algorithm for configuring a computeror processing circuitry, e.g., processor 24, to perform an exampleembodiment. In some cases, a general purpose computer may be providedwith an instance of the processor which performs the algorithm of arespective one of FIGS. 7 and 10 to transform the general purposecomputer into a particular machine configured to perform an exampleembodiment.

Accordingly, blocks of the flowchart support combinations of means forperforming the specified functions and combinations of operations forperforming the specified functions. It will also be understood that oneor more blocks of the flowchart, and combinations of blocks in theflowchart, can be implemented by special purpose hardware-based computersystems which perform the specified functions, or combinations ofspecial purpose hardware and computer instructions.

According to embodiments of the present invention, the interpretation ofcertain REs of a PRB as being muted, such as in accordance with PDSCH REmuting, by a first type of mobile terminal, such as a legacy mobileterminal, e.g., a mobile terminal operating in accordance with Release10 of the LTE specification, may be leveraged in order to increase thedensity within the PRB of the reference signal resource elements for asecond type of mobile terminals 10, such as mobile terminals configuredin accordance with Release 11 or beyond of the LTE specification. Theincreased density of the reference signal resource elements may provideincreased opportunities for the provision of channel state information,such as via CSI-RS, from the transmit point 14 to a the second type ofmobile terminal 10, without creating additional interference for thefirst type of mobile terminals, such as legacy mobile terminals.

As shown in FIG. 7 from the perspective of a second type of mobileterminal 10, such as mobile terminal configured to operate in accordanceRelease 11 or beyond of the LTE specification, the apparatus 20 of FIG.5 may include means, such as the processing circuitry 22, the processor24, the device interface 28 or the like, for receiving a definition of aplurality of resource elements of a physical resource block (PRB) to beallocated for the provision of channel state information referencesignals. In this regard, the plurality of resource elements allocatedfor the provision of channel state information reference signals may beresource elements that are allocated for CSI-RS, such as to providechannel estimation, interference information and the like. Thereafter,the apparatus may include means, such as the processing circuitry, theprocessor, the device interface or the like, for causing channel stateinformation estimation to be provided via the plurality of allocatedresource elements of the PRB, as shown in block 52 of FIG. 7.

In accordance with embodiments of the present invention, at least someof the plurality of resource elements of the PRB that are allocated forthe provision of channel state information reference signals correspondin position within the PRB to resource elements of the PRB that will beinterpreted by a different type of mobile terminal, e.g., the first typeof mobile terminal, to be muted so that the different type of mobileterminal receives its PDSCH accordingly. In one embodiment, for example,the different type of mobile terminal may be a legacy mobile terminal,such as a mobile terminal configured in accordance with Release 10 ofthe LTE specifications. In regard to the correspondence in position ofthe resource elements, at least some of the plurality of resourceelements of the PRB that are allocated for the provision of channelstate information reference signals may have identical positions withinthe PRB to the resource elements of the PRB that will be interpreted asbeing muted by a different type of mobile terminal. Thus, at least someof the resource elements that will be interpreted as CSI-RS by thesecond type of mobile terminal will be interpreted to be muted by adifferent type of mobile terminal, such as the first type of mobileterminal.

In one embodiment, some, but not all, of the plurality of resourceelements of the PRB that are allocated, from the perspective of thesecond type of mobile terminal, to the provision of channel stateinformation reference signals have identical positions within the PRB tothe resource elements of the PRB that will be interpreted as being mutedby the different type of mobile terminal. In this embodiment, some ofthe plurality of resource elements within the PRB may be interpreted byeach of the mobile terminals, such as the mobile terminals configured inaccordance with both Release 10 and Release 11 or beyond of the LTEspecifications, to be allocated for the provision of channel stateinformation reference signals. Thus, each of the plurality of resourceelements of the PRB that are allocated, from the perspective of thesecond type of mobile terminal, to the provision of channel stateinformation reference signals may have identical positions within thePRB to respective resource elements of the PRB that are interpreted by adifferent type of mobile terminal to be either muted or to also beallocated for the provision of channel state information referencesignals.

FIGS. 8A and 8B illustrate the same PRB with FIG. 8A depicting theinterpretation or definition of the PRB from the perspective of a firsttype of mobile terminal, such as a Release 10 mobile terminal, and FIG.8B depicting the interpretation or definition of the PRB from theperspective of a second type of mobile terminal, such as a Release 11 orbeyond mobile terminal. As shown in FIG. 8A, the PRB as interpreted by afirst type of mobile terminal, such as a Release 10 mobile terminal, mayinclude two resource elements that are interpreted to be muted.Additionally, the PRB of the first type of mobile terminal includes tworesource elements allocated for the provision of channel stateinformation reference signals, such as CSI-RS elements. Since thetransmit point 14 includes two transmit antennas in this embodiment, thePRB of the first type of mobile terminal includes two CSI-RS resourceelements.

Additionally, the PRB as interpreted by a mobile terminal 10 inaccordance with an example embodiment of the present invention, such asa second type of mobile terminal, e.g., a Release 11 or subsequentmobile terminal, is shown in FIG. 8B. In this regard, the PRB includes aplurality of resource elements that are allocated for the provision ofchannel state information reference signals, such as CSI-RS resourceelements. These CSI-RS resource elements are positioned in the samerelative position within the PRB as are the two resource elements thatare interpreted by the first type of mobile terminal as being muted, aswell as the two CSI-RS resource elements of the first type of mobileterminal.

Thus, a mobile terminal 10 in accordance with an embodiment of thepresent invention has the capacity to provide an increased number ofchannel state information reference signals since the PRB of the mobileterminal includes more resource elements allocated for the provision ofchannel state information reference signals than in the case of othermobile terminals, such as legacy Release 10 mobile terminals. However,by positioning resource elements that support the additional channelstate information reference signals for a second type of mobile terminalcoincident with the resource elements within the PRB that areinterpreted by a first type of mobile terminal to be muted, the firsttype of mobile terminal will not monitor the channel state informationreference signals provided by the mobile terminal in accordance with anexample embodiment of the present invention within the correspondingmuted resource elements, thereby avoiding interference or otherconfusion.

In one embodiment, at least some of the plurality of reference signalresource elements of the PRB of the mobile terminal 10 of the exampleembodiment of the present invention are spaced uniformly within the PRB.As shown in FIG. 8B, for example, the resource elements that areallocated for channel state information reference signals are evenlyspaced in frequency so as to facilitate provision of channel stateinformation reference signals. Alternatively, the reference signalresource elements may be staggered within the PRB so as not to beuniformly spaced within the PRB.

As another example, FIGS. 9A and 9B illustrate the same PRB with FIG. 9Adepicting the interpretation or definition of the PRB from theperspective of a first type of mobile terminal, such as a Release 10mobile terminal, and FIG. 9B depicting the interpretation or definitionof the PRB from the perspective of a second type of mobile terminal,such as a Release 11 mobile terminal. With reference to FIG. 9A, the PRBmay be interpreted by a first type of mobile terminal, such as a legacymobile terminal, to include a plurality of resource elements allocatedfor the provision of channel state information reference signals, suchas CSI-RS resource elements, and a plurality of resource elements thatare muted. As shown in FIG. 9B, the PRB may be interpreted by a mobileterminal 10 of an example embodiment of the present invention to includereference signal resource elements that correspond, such as by beingidentically positioned within the PRB, to resource elements of the PRBthat are interpreted by the first type of mobile terminal to be muted.In contrast to the embodiment of FIG. 8B, the embodiment of FIG. 9Bdefines the resource elements of the PRB, as interpreted by the mobileterminal of the example embodiment, that are allocated for the provisionof channel state information reference signals, such as by havingidentical positions, to the resource elements of the PRB that areinterpreted by the first type of mobile terminal to be muted. In thisregard, the PRB as interpreted by the mobile terminal of the exampleembodiment does not define any resource elements that are allocated forthe provision of channel state information reference signals to bepositioned so as to correspond with the resource elements of the PRBthat are interpreted by the first type of mobile terminal to also beallocated for the provision of channel state information referencesignals. Instead, the PRB, as interpreted by the mobile terminal of theexample embodiment, may interpret the resource elements that docorrespond, such as by being identically positioned within the PRB, tothe resource elements that are interpreted by the first type of mobileterminal to be allocated for the provision of channel state informationreference signals to be muted so as to avoid any interference orconfusion therebetween.

As shown in FIG. 10 from the perspective of a transmit point 14, a basestation or other network entity, the apparatus 40 may include means,such as the processing circuitry 42, the processor 44 or the like, forseparately defining the manner in which a physical resource block is tobe interpreted by a first type of mobile terminal, such as a legacymobile terminal, e.g., a mobile terminal configured in accordance withRelease 10 of the LTE specification, and by a second type of mobileterminal, such as a mobile terminal in accordance with Release 11 orsubsequent releases of the LTE specification. As shown in block 60 ofFIG. 10, the apparatus may include means, such as the processingcircuitry, the processor or the like, for defining one or more firstresource blocks of the PRB to be allocated for the provision of channelstate information reference signals from the first type of mobileterminal. For example, the first type of mobile terminal may interpretthe PRB so as to define one or more CSI-RS resource elements.

Additionally, the apparatus 40 may include means, such as the processingcircuitry 42, the processor 44 or the like, for defining one or moresecond resource elements of the PRB that are interpreted by the firsttype of mobile terminal to be muted. See block 62 of FIG. 10.Additionally, the apparatus of this embodiment may include means, suchas the processing circuitry, the processor or the like, for defining aplurality of resource elements of the PRB to be allocated for theprovision of channel state information reference signals from a secondtype of mobile terminal, such as a mobile terminal 10 configured tooperate in accordance with Release 11 of the LTE specification. Seeblock 64 of FIG. 10. In this regard, these allocated resource elementsof the PRB may correspond in position to the second resource elements ofthe PRB as interpreted by the first type of a mobile terminal, such asdescribed above in conjunction with FIGS. 7-9. As described above, theresource elements of the PRB that are allocated for the provision ofchannel state information reference signals from the second type ofmobile terminal may all be positioned so as to correspond, such as bybeing identically positioned within the PRB, to the second resourceelements of the PRB that are interpreted by the first type of mobileterminal to be muted. Or, some of the resource elements of the PRB thatare allocated for the provision of channel state information referencesignals from the second type of mobile terminal may be positioned so asto correspond, such as by being identically positioned, to the secondresource elements of the PRB that are interpreted by the first type ofterminal to be muted, while other resource elements of the PRB that areallocated for the provision of channel state information from the secondtype of mobile terminal may be positioned so as to correspond, such asby being identically positioned, with the first and/or second resourceelements of the PRB, such as shown in FIG. 9B.

By aligning the resource elements of the PRB that are allocated for theprovision of channel state information reference signals from the secondtype of mobile terminal 10 with resource elements of the PRB that areinterpreted by the first type of mobile terminal to be either muted orto also be allocated for the provision of channel state informationreference signals, the methods, apparatus and computer program productsof embodiments of the present invention may reduce or eliminateinstances in which interference or other confusion is created byavoiding or preventing receipt of the channel state informationreference signals from the second type of mobile terminal by the firsttype of mobile terminal.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A method of configuring resource elements for the provision ofchannel state information reference signals, the method comprising:receiving a definition of a plurality of resource elements of a physicalresource block (PRB) to be allocated for the provision of channel stateinformation reference signals for a mobile terminal, wherein at leastsome of the plurality of resource elements of the PRB that are allocatedfor the provision of channel state information reference signalscorrespond in position to resource elements of the PRB that areconfigured to be interpreted as muted by a different type of mobileterminal; and receiving channel state information reference signals viathe plurality of resource elements of the PRB that are allocated for theprovision of channel state information reference signals, wherein someof the plurality of resource elements of the PRB that are allocated forthe provision of channel state information reference signals haveidentical positions within the PRB to resource elements of the PRB thatare configured to be interpreted by the different type of mobileterminal as allocated for provision of channel state informationreference signals for the different type of mobile terminal. 2.(canceled)
 3. (canceled)
 4. A method according to claim 1, wherein eachof the plurality of resource elements of the PRB that is allocated forthe provision of channel state information reference signals has anidentical position within the PRB to a respective resource element ofthe PRB that is configured to be, interpreted by the different type ofmobile terminal to be either muted or allocated for provision of channelstate information reference signals for the different type of mobileterminal.
 5. A method according to claim 1, wherein the channel stateinformation reference signals that correspond in position to resourceelements of the PRB that are configured to be interpreted as muted bythe different type of mobile terminal have a greater density thanresource elements of the PRB that are allocated for channel stateinformation reference signals for the different type of mobile terminal.6. A method according to claim 1 wherein at least some of the pluralityof resource elements of the PRB are spaced uniformly within the PRB. 7.A method according to claim 1 wherein at least some of the plurality ofresource elements of the PRB are nonuniformly spaced within the PRB. 8.Apparatus for configuring resource elements for the provision of channelstate information reference signals, the apparatus comprising aprocessing system arranged to: receive a definition of a plurality ofresource elements of a physical resource block (PRB) to be allocated forthe provision of channel state information reference signals for amobile terminal, wherein at least some of the plurality of resourceelements of the PRB that are allocated for the provision of channelstate information reference signals correspond in position to resourceelements of the PRB that are configured to be interpreted as muted by adifferent type of mobile terminal; and receive channel state informationreference signals to be received via the plurality of resource elementsof the PRB that are allocated for the provision of channel stateinformation reference signals, wherein some of the plurality of resourceelements of the PRB that are allocated for the provision of channelstate information reference signals have identical positions within thePRB to resource elements of the PRB that are configured to beinterpreted by the different type of mobile terminal as allocated forprovision of channel state information reference signals for thedifferent type of mobile terminal.
 9. (canceled)
 10. (canceled)
 11. Anapparatus according to claim 8 wherein each of the plurality of resourceelements of the PRB that is allocated for the provision of channel stateinformation reference signals has an identical position within the PRBto a respective resource element of the PRB that is configured to beinterpreted by the different type of mobile terminal to be either mutedby the different type of mobile terminal or allocated for provision ofchannel state information reference signals by the different type ofmobile terminal.
 12. An apparatus according to claim 8 wherein thechannel state information reference signals that correspond in positionto resource elements of the PRB that are configured to be interpreted asmuted by the different type of mobile terminal have a greater densitythan resource elements of the PRB that are allocated for channel stateinformation reference signals for the different type of mobile terminal.13. An apparatus according to claim 8, wherein at least some of theplurality of resource elements of the PRB are spaced uniformly withinthe PRB.
 14. An apparatus according to claim 8 wherein at least some ofthe plurality of resource elements of the PRB are non-uniformly spacedwithin the PRB.
 15. An apparatus according to claim 8 wherein theapparatus comprises a mobile terminal.
 16. An apparatus according toclaim 15 comprising a device interface configured to communicate with abase station in order to receive the definition of the plurality ofresource elements of the PRB to be allocated for provision of channelstate information reference signals.
 17. An apparatus according to claim15, wherein the processing system is configured for use in a Long TermEvolution (LTE) system.
 18. A method of configuring resource elementsfor the provision of channel state information reference signals, themethod comprising: defining one or more first resource elements of aphysical resource block (PRB) to be allocated for the provision ofchannel state information reference signals for a first type of mobileterminal; defining one or more second resource elements of the PRB to beinterpreted as muted by the first type of mobile terminal; and defininga plurality of resource elements of the PRB to be allocated forprovision of channel state information reference signals for a secondtype of mobile terminal, wherein at least some of the plurality ofresource elements of the PRB that are allocated for the provision ofchannel state information reference signals for the second type ofmobile terminal correspond in position to the second resource elementsof the PRB, and wherein some of the plurality of resource elements ofthe PRB that are allocated for the provision of channel stateinformation reference signals for the second type of mobile terminalhave identical positions within the PRB to the first resource elementsof the PRB.
 19. (canceled)
 20. (canceled)
 21. A method according toclaim 18, wherein each of the plurality of resource elements of the PRBthat is allocated for the provision of channel state informationreference signals for the second type of mobile terminal has anidentical position within the PRB to a respective one of the first orsecond resource elements of the PRB.
 22. A method according to claim 18,wherein the channel state information reference signals that correspondin position to resource elements of the PRB that are configured to beinterpreted as muted by the first type of mobile terminal have a greaterdensity than resource elements of the PRB that are allocated for channelstate information reference signals for the first type of mobileterminal.
 23. A method according to claim 18 wherein defining theplurality of resource elements of the PRB as interpreted by the secondtype of mobile terminal comprises spacing at least some of the resourceelements uniformly within the PRB.
 24. A method according to claim 18wherein defining the plurality of resource elements of the PRB asinterpreted by the second type of mobile terminal comprises spacing atleast some of the resource elements nonuniformly within the PRB. 25.Apparatus for configuring resource elements for the provision of channelstate information reference signals, the apparatus comprising aprocessing system arranged to: define one or more first resourceelements of a physical resource block (PRB) to be allocated for theprovision of channel state information reference signals for the firsttype of mobile terminal; define one or more second resource elements ofthe PRB to be interpreted as muted by the first type of mobile terminal;and define a plurality of resource elements of the PRB to be allocatedfor provision of channel state information reference signals for asecond type of mobile terminal, wherein at least some of the pluralityof resource elements of the PRB that are allocated for the provision ofchannel state information reference signals for the second type ofmobile terminal correspond in position to the second resource elementsof the PRB, and wherein some of the plurality of resource elements ofthe PRB that are allocated for the provision of channel stateinformation reference signals for the second type of mobile terminalhave identical positions within the PRB to the first resource elementsof the PRB.
 26. (canceled)
 27. (canceled)
 28. An apparatus according toclaim 25, wherein each of the plurality of resource elements of the PRBthat is allocated for the provision of channel state informationreference signals for the second type of mobile terminal has anidentical position within the PRB to a respective one of the first orsecond resource elements of the PRB.
 29. An apparatus according to claim25 wherein the channel state information reference signals thatcorrespond in position to resource elements of the PRB that areconfigured to be interpreted as muted by the first type of mobileterminal have a greater density than resource elements of the PRB thatare allocated for channel state information reference signals by thefirst type of mobile terminal.
 30. An apparatus according to claim 25,wherein the processing system is arranged to define the plurality ofresource elements of the PRB as interpreted by the second type of mobileterminal by spacing at least some of the resource elements uniformlywithin the PRB of the second type of mobile terminal.
 31. An apparatusaccording to claim 25, wherein the processing system is arranged todefine the plurality of resource elements of the PRB as interpreted bythe second type of mobile terminal by spacing at least some of theresource elements nonuniformly within the PRB of the second type ofmobile terminal.
 32. An apparatus according to claim 25 wherein theapparatus comprises a base station.
 33. An apparatus according to claim32, comprising a device interface configured to communicate with aplurality of mobile terminals including provision of definitions of thePRBs to the first and second types of mobile terminals.
 34. An apparatusaccording to claim 32, wherein the processing system is configured foruse in a Long Term Evolution (LTE) system.
 35. A computer readablemedium comprising a set of instructions, which, when executed by acomputing system, cause the computing system to perform the steps of:receiving a definition of a plurality of resource elements of a physicalresource block (PRB) to be allocated for the provision of channel stateinformation reference signals for a mobile terminal, wherein at leastsome of the plurality of resource elements of the PRB that are allocatedfor the provision of channel state information reference signalscorrespond in position to resource elements of the PRB that areconfigured to be interpreted as muted by a different type of mobileterminal; and receiving channel state information reference signals viathe plurality of resource elements of the PRB that are allocated for theprovision of channel state information reference signals, wherein someof the plurality of resource elements of the PRB that are allocated forthe provision of channel state information reference signals haveidentical positions within the PRB to resource elements of the PRB thatare configured to be interpreted by the different type of mobileterminal as allocated for provision of channel state informationreference signals for the different type of mobile terminal.
 36. Acomputer readable medium comprising a set of instructions, which, whenexecuted by a computing system, cause the computing system to performthe steps of: defining one or more first resource elements of a physicalresource block (PRB) to be allocated for the provision of channel stateinformation reference signals for a first type of mobile terminal;defining one or more second resource elements of the PRB to beinterpreted as muted by the first type of mobile terminal; and defininga plurality of resource elements of the PRB to be allocated forprovision of channel state information reference signals for a secondtype of mobile terminal, wherein at least some of the plurality ofresource elements of the PRB that are allocated for the provision ofchannel state information reference signals for the second type ofmobile terminal correspond in position to the second resource elementsof the PRB, and wherein some of the plurality of resource elements ofthe PRB that are allocated for the provision of channel stateinformation reference signals for the second type of mobile terminalhave identical positions within the PRB to the first resource elementsof the PRB.